The invention is directed generally to electrochemical apparatus for the oxidation or consumption of a fuel and the generation of electricity, such as electrochemical reactors and molten salt or solid electrolyte fuel cells.
Although applicable to conventional cofired or tubular apparatus, the present invention is particularly useful when incorporated into solid oxide fuel cells, preferably noncofired and planar, that contain a stack of multiple assemblies. Each assembly comprises a solid electrolyte disposed between a cathode and an anode, being bounded by separators which contact the surfaces of the electrodes opposite the electrolyte. A fuel manifold and an air manifold pass gases through or over the assembly elements, with a gasket sealing the anode adjacent to the air manifold and a gasket sealing the cathode adjacent to the fuel manifold to minimize fuel and air mixing in a zone which would decrease cell voltage.
The fuel cell operates by the introduction of air into the cathode and the ionization of oxygen at the cathode/electrolyte surface. The oxygen ion moves across the gas-nonpermeable electrolyte to the anode interface, where it reacts with the fuel flowing into the anode, releasing heat and giving up its electron to the anode. The electron passes through the anode and separator to the next adjacent cathode.
Any clean hydogen- or hydrocarbon-containing fuel can be used in the electrochemical apparatus of the present invention, such as hydrogen, carbon monoxide, methane, natural gas, and reformed hydrocarbon fuels. The gas to be supplied to the cathode can be oxygen or an oxygen-containing gas such as air, NO.sub.x, or SO.sub.x.
The solid electrolyte surface may be coated or "painted" with an ink, or a thin layer of the composition that comprises the cathode, on the surface adjacent to the cathode, and with a nickel or nickel oxide ink (or other anode material) on the surface adjacent to the anode. The painted ink provides an environment for electrical conduction and in which the species can interact (molecular/ionic) or react (molecular/atomic).
A solid electrolyte fuel cell and assembly containing a plurality of fuel cells is disclosed in U.S. Pat. No. 4,770,955 to Ruhl, which is hereby incorporated by reference as if fully written out below. Ruhl discloses a fuel cell for oxidizing a fuel to produce electrical energy comprising the following elements.
--A plate-like, gas-impervious separator including a first internal hole passing through the first separator for receiving a gaseous fuel. PA1 --A plate-like oxide powder cathode in contact with the first separator and including a second internal hole passing through the cathode for receiving a gaseous fuel, the second hole being in at least partial registration with the first hole. PA1 --A plate-like, gas-impervious solid electrolyte in contact with the cathode and including a third internal hole passing through the electrolyte the third hole being in at least partial registration with the first hole. PA1 --A substantially gas-impervious tubular gasket disposed within the second hole and sealingly contacting the electrolyte to protect the cathode from fuel within the first hole. PA1 --A plate-like powder anode in contact with the solid electrolyte and including a fourth internal hole passing through the anode, the fourth hole being in at least partial registration with the first hole.
An embodiment of the Ruhl fuel cell is also disclosed in which the separator, cathode, electrolyte and anode, respectively include fifth, sixth, seventh and eighth holes for receiving an oxygen-bearing gas, the sixth, seventh, and eighth holes each being in at least partial registration with the fifth hole, and a substantially gas-impervious tubular gasket is disposed within the eighth hole and sealingly contacting the electrolyte to protect the anode from oxygen within the fifth hole.
The Ruhl fuel cell represents a significant step in the advancement of the art, being directed to non co-sintered elements which provide ease of fabrication as well as extended life due to the ability of the elements to accommodate their differing thermal expansion properties.
Cermet electrodes for solid oxide electrochemical fuel cells, preferably tubular in shape, are disclosed in U.S. Pat. No. 4,582,766 to Isenberg et at. Electronic conductors (metals) form the electrode and are bound to the electrolyte by a ceramic coating which is preferably the same material as the electrolyte. The metal electrode particles are oxidized and then reduced to form a porous metal layer which contacts both the ceramic coating and the metal electrode particles. The problems of ceramic-metal thermal expansion mismatch are not solved, and are indeed increased by the electrolyte/electrode bound structure. Further, the design of the electrode itself is not altered to provide an enhancement of flow characteristics across it.